Hysteresis heating unit

ABSTRACT

A heating unit in the form of a flat hotplate or boxlike oven in which heat is generated by hysteresis. A ferromagnetic core in the form of a flat panel or three-dimensional container is wound with a coil of electrically conductive material fitted with means for connection to a source of alternating current. The coil may be wound around a three-dimensional core or wound as a flat spiral on one surface of the core. The heating unit is operated by alternate magnetization and demagnetization of the ferromagnetic core to generate heat by hysteresis. One example of use of such a hysteresis heating unit is a portable oven for use in delivery of hot food and adapted for operation from the alternator of a mobile vehicle.

United States Patent r e h ou r .mT S 0 7 [72] Inventor LeonR.Lense 1,023,791 4/1912 Anderson.....................

c/oElectrol Equipment Incorporated, Box 1,995,811 3/1935 1209, Mankato, Minn. 56001 3,5 30,499 12,736

[21] Appl. No. [22] Filed Feb. 19, 1970 [45] Patented Jan. 4, 1972 Assistant Examiner-Hugh D. Jaeger AtmrneyBurd, Braddock & Bartz ABSTRACT: A heating unit in the form of a flat hotplate or boxlikc oven in which heat is generated by hysteresis. A ferromagnetic core in the form of a flat panel or three-dimensional container is wound with a coil of electrical! o 1 W l 2 H N U mm F g m 1 E I v 0 5 H6 U M m H w [51] Int. H051) 5/00, y conductive with means for connection to a source of alter- HOSb 9/00 material fitted nating current.

Field 219/1049, The coil may be wound around a three-dimendYSd. mnbnne nalfia nww .m m v eamee o fl f awne OhmVn t. 00 m d e okhn um w o a u n D. r t Ogmo en.l .p cu 01 a fl e e e a a m e man w mv kmum 9 M 0 40 1 m9 ,1 92 l 2 S T N E T A P" Sm M n n A m a m T m m fist]. eD uo GH H 18 N w% 11 NW 38 67 5 .l 3% 6 5 48 ..l

PATENTED JAN 4 I972 SHEET 1 0F 2 INVE-N'TOR. LEON R. LEASE ATTORNEYS PATENTED JAN 4 I972 SHEET 2 [IF 2 [.VVENTOR. LEON R. LEASE AT TORNEYS HYSTERESIS HEATING UNIT This invention relates to heating units, such as hotplates, warming trays, ovens and the like, in which heat is generated as a result of the effect of hysteresis in a ferromagnetic core in the form of a sheet, plate or box. Magnetization is believed to consist in breaking up and reorienting certain molecular groupings. Because the molecules tend to want to stay undisturbed, all substances offer some resistance to magnetization. Similarly, once magnetized they resist demagnetization. When a ferromagnetic core is magnetized by passing a current of electricity around it in one direction, it is demagnetized by passing a current of electricity around it in the opposite direction to the current that magnetized it. Hysteresis is the lag of magnetic induction behind magnetizing force. The energy that is expended in overcoming hysteresis appears in the core as heat. The present invention is based upon the generation of heat by the rapid alternating magnetization and demagnetization of a ferromagnetic core in which the magnetic lag is relatively high.

The invention is illustrated in the accompanying drawings in which the same numerals are used to identify corresponding parts and in which:

FIG. 1 is an isometric view of a portable oven embodying the invention and shown with a part broken away to reveal interior construction;

FIG. 2 (appearing on sheet 2 of the drawings) is an end elevation, partly broken away and in section, of the oven of FIG. 1;

FIG. 3 (appearing on sheet 2 of the drawings) is a top plan view, partly broken away and in section, of the oven of FIG. 1;

FIG. 4 is a schematic diagram illustrating the circuitry embodied in the oven; and

FIG. 5 is a schematic representation of an alternative form of unit for producing heat by hysteresis.

Referring now to the drawings, and particularly to FIGS. 1, 2 and 3, there is shown a portable oven, indicated generally at 10, such as used for delivery of foods such as pizza, chicken, ribs, chow mein, and the like. Such foods are often ordered by telephone for home delivery while still hot for immediate consumption. The oven is generally boxlike having an outer shell including sidewalls l1 and 12, rear wall 13, top wall 14 and bottom wall 15. The outer shell may be formed from sheet metal, rigid plastic sheeting, molded from plastic or the like. It encloses a similar boxlike inner shell, indicated generally at 16, of slightly smaller dimensions and composed of ferromagnetic material such as relatively thin sheet iron or steel. The inner shell 16 likewise includes sidewalls l7 and 18, rear wall 19, top wall 20 and bottom wall 21. As illustrated, the forward edges of the side, top and bottom walls 17, 18, 20 and 21, respectively, of the inner shell are provided with outwardly extending flanges 22 which function as spacer members for the inner shell and form a shoulder spaced from the open front edges of the outer shell in a recess which receives a door 23.

Recessed door 23 includes an outer front wall 24 and an inner front wall 25, one of which is provided with a peripheral flange 26 which serves as a spacer means and edge closure means for the door. Door 23 is preferably hinged at 27 to the bottom wall of the outer shell. The door is provided with a handle 28 and a catch 29 which is engaged by a latch 30 to hold the door closed.

As best seen in conjunction with the schematic circuit diagram of F IG. 4, the inner shell 16 of ferromagnetic material is the heating element. It is wound with a helical coil having a plurality of turns of insulated electrical conductor wire 31. The turns of the coil are spaced, for example, from about oneeighth to one-half inch or so apart. While the conductor wire 31 is preferably insulated, bare wire may be used provided it is insulated from the ferromagnetic core 16, as by thin sheets or spacer bars of electrical insulating material. The shell is the heating element. While the wire may get hot, this does not necessarily occur and this is not relied upon as a primary source of heat.

The space between the inner and outer oven shells and between the inner and outer walls of the door 23 are filled with heat insulating material 32, such as Fiberglas, rigid cellular polystyrene, polyurethane, or the like, preferably foamed in place, and similar heat-insulating substances. This insulation is desirably of the order of about three-fourths to 1% inches in thickness, sufficient to efficiently insulate the oven without unduly adding to its overall size.

The helical coil of wire 31 is connected to the terminals of a socket 33 adapted to receive a plug 34 connected by the wires 35 of an extension cord for connection to a source 36 of alternating current. For the home delivery of hot food, the source 36 of alternating current is desirably the alternator of the delivery car, station wagon or truck. The unit is desirably also adapted to be connected through an appropriate transformer to an electrical outlet of any industrial or commercial alternating current power source. For example, the oven may be preheated and stocked while connected to a kitchen outlet and then connected to the mobile alternator while the delivery boy makes the rounds of his delivery routes.

The circuit is controlled by a thermostatic switch 37 or similar heat-responsive control means to maintain some predetermined temperature level. Desirably, the circuit includes a pair of pilot lights. One light 38 signals that'the oven is turned on," that is, plugged in, and the other light 39 signals that the circuit is heating, that is, the thermostatic switch 37 is closed. Latch 30, socket 33 and pilot lights 38 and 39 are desirably housed in a superstructure 40 mounted on the top of the outer oven shell. An on-off switch may obviously be included in the circuit if desired. However, for a portable oven for fast delivery of hot foods, this is generally unnecessary because the oven will ordinarily be turned on and off by connecting to and disconnecting from the alternator as it is moved into the car for deliveries and returned to the kitchen for restocking. The size of the oven may vary greatly. A pizza delivery oven typically has inside dimensions about i472 by 14% inches and as high as desired.

Referring to FIG. 5, there is shown an alternative means of construction by which the hysteresis heating effect can be obtained. There is shown a flat rectangular sheet of ferromagnetic material such as sheet steel, indicated generally at 4l, and divided by fold lines 42-44 into four panels 45-48 which when folded will form the first sidewall panel, bottom wall panel, second sidewall panel and top wall panel, respectively, of the inner shell liner of an oven.

Each of panels 45-47 is provided with a flat spiral coil 49-51 of electrically conductive material affixed' to the surface of the panels but electrically insulated from the ferromagnetic material from which the panels are formed. The coils 49-51 may be formed from insulated wire affixed, as by taping or the like, to the panels, or stamped from a thin sheet of electrically conductive material and adhesively adhered to the panels, or the like. Preferably, they are formed as a printed circuit by silk screening or othermeans onto the surfaces of the ferromagnetic panels which have'first been given an insulating coating of porcelain enamel or the like.

Coil 49 is provided with a lead-in conductor in the form of insulated wire 52. Coils 49 and 50 are electrically connected by means of a lengthof insulated wire 53, as are coils 50 and 51 by means of insulated wire 54. A lead-out conductor 55 is connected to the other end of coil 51. Panel 48 to form the top wall of the inner shell and an appropriate rear wall panel may be provided with a heating coil if desired, but this is generally unnecessary. For assembly of the oven, panel 41 is bent along the fold lines as indicated with the coils 4951 onthe exterior surfaces so as to lie in the space between the inner and outer shells in the assembled oven.

For the transporting of hot food, which is ordinarily boxed, shelves within the oven are generally unnecessary. This means that the interior of the oven is defined by flat panels easy to clean and maintain. However, if desired, shelves may be incorporated into the oven design and, if desired, the shelves may be utilized as heating elements. Likewise, the inner door panel can be heated or not as desired. The liner walls may be very thin when rigid foam is used as the heat insulator as the insulation then provides the necessary strength and rigidity.

Since the amount of heat generated is proportional to the intensity of the magnetic field applied to the liner, the magnetic coupling between the applied field and the liner, the frequency of inversion of the magnetic field and the area enclosed in the hysteresis or magnetization curve of the material used as the liner, the oven may be designed and operated over a wide range of temperatures. Thus, the oven may be utilized as a warming oven, for keeping already hot foods at some predetermined temperature, or as a cooking oven. In the latter instance, food delivery can be expedited since the food may be cooked while in transit. Such ovens are readily adapted for use in mobile homes, motor homes, campers, and the like. Such ovens are also adapted for use in commercial airliners to cook or maintain hot food for passengers. They are likewise adapted for use in food carts used in hospitals, industrial plants, and the like, to maintain food warm until served.

Although the invention has been described in detail in connection with its use in ovens, it is adapted to use in a wide variety of forms such as heatable appliances, cooking pans, coffee makers, bottle warmers, and the like. For example, the heating unit may take the form of a double-walled warming or cooking pot in which the helix of conducting wire is disposed on the outside surface of an inner liner of ferromagnetic material, or it may take the form of a hotplate, warming tray or heating panel. For this use, the preferred structure is that of FIG. 5 wherein the electrical conductor is disposed in the form of a flat spiral coil opposite from the surface to be exposed. A cooking stove may be constructed by disposing a plurality of such soils, corresponding to several conventional burners, on the under surface of a porcelain enameled steel panel. The unobstructed flat top cooking surface is easy to use and to maintain.

it is apparent that many modifications and variations of this invention as hereinbefore set forth may be made without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only and the invention is limited only by the terms of the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A portable hysteresis oven for use in automotive vehicles comprising:

A. a three-dimensional thin-walled ferromagnetic container in the form of a box of rectangular cross section closed at one end,

B. at least one coil of electrically conductive material wound about the exterior surface of said container in a closely spaced magnetic coupling with the container and electrically insulated therefrom, each coil comprising a single winding and the turns of said coil being spaced apart between about one-eighth to one-half inch,

C. means for connecting the ends of said coil to the alternator of an automotive vehicle as a source of alternating electric current, whereby upon rapid alternating magnetization and demagnetization of the ferromagnetic container heat is generated in the container by hysteresis,

D. an outer protective shell surrounding said container, said outer shell being of generally the same configuration as said container with greater dimensions sufficient to provide a substantially uniform space between about threefourths and 1% inches thick between the container and shell,

E. protective heat insulative material disposed over said coil within said shell to substantially fill the space between said container and outer shell,

F. heat-responsive control means for regulating flow of current to said coil to maintain substantially uniform heat in said container, and

G. a double-walled heat insulated door hinged along one side of the open end of the oven to provide a closure for the open end of said container. v 2. An oven according to claim 1 further characterized in that said coil is in the form of a helix extending around said container.

3. An oven according to claim 1 further characterized in that said coil is in the form of a flat spiral affixed to the surface of said container.

4. An oven according to claim 1 further characterized in that:

A. said core is a generally two-dimensional panel,

B. said coil is in the form of a fiat spiral affixed to but electrically insulated from the surface of said panel, and

C. a lead-in conductor electrically insulated from said coil is connected to the innermost end of the fiat spiral coil.

5. An oven according to claim 4 further characterized in that:

A. said panel is coated with a thin surface layer of electrically insulating material, and

B. said coil is imprinted on the surface of said insulating material.

6. An oven according to claim 4 further characterized in that:

A. said panel is steel having a porcelain enamel coating on both sides,

B. said coil is a silk screen imprinted circuit disposed on the surface of the enamel coating, and

C. said lead-in conductor is an insulated wire overlying the printed circuit. 

1. A portable hysteresis oven for use in automotive vehicles comprising: A. a three-dimensional thin-walled ferromagnetic container in the form of a box of rectangular cross section closed at one end, B. at least one coil of electrically conductive material wound about the exterior surface of said container in a closely spaced magnetic coupling with the container and electrically insulated therefrom, each coil comprising a single winding and the turns of said coil being spaced apart between about oneeighth to one-half inch, C. means for connecting the ends of said coil to the alternator of an automotive vehicle as a source of alternating electric current, whereby upon rapid alternating magnetization and demagnetization of the ferromagnetic container heat is generated in the container by hysteresis, D. an outer protective shell surrounding said container, said outer shell being of generally the same configuration as said container with greater dimensions sufficient to provide a substantially uniform space between about three-fourths and 1 1/2 inches thick between the container and shell, E. protective heat insulative material disposed over said coil within said shell to substantially fill the space between said container and outer shell, F. heat-responsive control means for regulating flow of current to said coil to maintain substantially uniform heat in said container, and G. a double-walled heat insulated door hinged along one side of the open end of the oven to provide a closure for the open end of said container.
 2. An oven according to claim 1 further characterized in that said coil is in the form of a helix extending around said container.
 3. An oven according to claim 1 further characterized in that said coil is in the form of a flat spiral affixed to the surface of said container.
 4. An oven according to claim 1 further characterized in that: A. said core is a generally two-dimensional panel, B. said coil is in the form of a flat spiral affixed to but electrically insulated from the surface of said panel, and C. a lead-in conductor electrically insulated from said coil is connected to the innermost end of the flat spiral coil.
 5. An oven according to claim 4 further characterized in that: A. said panel is coated with a thin surface layer of electrically insulating material, and B. said coil is imprinted on the surface of said insulating material.
 6. An oven according to claim 4 further characterized in that: A. said panel is steel having a porcelain enamel coating on both sides, B. said coil is a silk screen imprinted circuit disposed on the surface of the enamel coating, and C. said lead-in conductor is an insulated wire overlying the printed circuit. 